The tobacco specific nitrosamines, N'-nitrosonornicotine (NNN), and 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) occur in unburned tobacco and mainstream and sidestream tobacco smoke in high concentrations and are carcinogenic in experimental animals. Therefore, these nitrosamines may be causative factors in tobacco related cancers, which have been estimated to comprise more than one-third of the cancers occurring in U.S. males. It is the objective of this proposal to determine the mechanism of action of these major environmental carcinogens through studies of metabolism and binding to cellular macromolecules and to establish the basis for their organ-specific effects. The structures of the NNN-DNA and NNK-DNA adducts formed after administration to rats or hamsters of specifically labelled NNN or NNK will be determined using chromatographic and spectroscopic methods, as well as synthetic marker compounds. The formation and persistence of these adducts, as well as the rates of activation and detoxification in target and non-target organs will be measured. The effects of potential chemopreventive agents on the carcinogenicity of NNN will be determined through metabolic studies and bioassays in rats. The metabolism of NNN and NNK in smokers will also be investigated. These goals are important for a better understanding of the tobacco related cancers and the mechanisms of nitrosamine carcinogenesis.